The present invention relates to a convergence correction system for a CRT display apparatus such as a color TV set, a display, and a projection TV set for correcting misconvergence using a digital memory and more particularly to a convergence correction system with recovery function for correcting misconvergence using a photo detector and a display apparatus using it.
In a color projection display apparatus using a plurality of projection tubes, misconvergence is generated on the display screen because the incident angle to the screen varies with each projection tube. To correct this misconvergence precisely on the screen, a convergence correction system is used. For example, Japanese Patent Application Laid-Open Sho 57-212492 discloses a digital convergence correction system which can adjust convergence with high precision. However, it is not taken into account in the above correction system that there is a possibility that the convergence changes due to geomagnetism and temperature after convergence adjustment. If this occurs, it is necessary to adjust the convergence each time. Therefore, for example, an apparatus for automatically correcting this misconvergence is proposed in Japanese Patent Application Laid-Open Sho 63-209388.
As a method for detecting misconvergence, in the aforementioned conventional example, a method that a light-position sensor using a detection device having a position calculation function, for example, a semiconductor light-position sensor is arranged in the overscanned area is used. However, a light-position sensor is generally expensive. On the other hand, for example, as an art indicated in Japanese Patent Application Laid-Open Sho 63-224572, a method that a plurality of inexpensive photoelectric devices which are neighboring to each other detect in the same way as a light-position sensor is known. However, to correct misconvergence with high precision, it is necessary to detect it at a plurality of positions and arrange many photoelectric devices. As a result, a problem arises that the number of connected lines increases and the control becomes complicated.